<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
        <style>
            .demo{
                background-color: yellow;
            }
        </style>
    </head>
    <body>
        <button id="btn">点击创建input并获取焦点</button>
        <script>
            const btn = document.getElementById('btn');
            btn.onclick = function(){
                const input = document.createElement('input');
                input.className ='demo';
                input.value = 99;
                input.onclick = ()=>{
                    alert(1);
                }
                console.log(input.parentElement)//这里获取不到父元素   null
                document.body.appendChild(input);
                input.focus();
                input.parentElement.style.backgroundColor = 'skyblue'
            }
        </script>
    </body>
</html>